[Collins] 32S-1 PLATE CURRENT

[Dr. Gerald N. Johnson, electrical engineer]

As far as I know there is no TIME stability problem with the
neutralization of 6146B. Some circuits don't have the range because its
capacitances are different from the smaller tubes.

Likely the tubes are gassy. Check to see that the bias voltage you read
on the voltmeter is really DC. The bias filter capacitor could easily be
open. The bias rectifier in the power supply is always suspect. Its a
tiny selenium that wasn't much good when it was new and its grown poorer
with age. Both series resistance and leakage can have increased
significantly.

Check the bias voltage near the tube grids. The voltage there should
reach at least 50 or 60 volts with the power supply voltage at 140
because it takes nearly that to shut off the PA tubes.

Check the meter shunt, it could be giving an erroneous indication of
plate current. Or a soldered connecting in that circuit could be faulty
causing the increased voltage drop to the meter that varies.

There might be some indications of output while setting the bias if the
PA or driver is oscillating.

Check the screen voltage. High screen voltage will cause high plate
current.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.